Ditto McLernon's thoughts, mounting a scope just doesn't get any better that with Burris Sig Zees. Ask Lik2hunt what he thinks about em, the Japan built Tasco scope I just sold him had only been mounted in Sig Zees, not a mark on it, and it had been mounted on at least 2 different rifles after I got it.
Mediums will usually work, just depends on the scope, usually with a little judicious dremel trimming of the hammer spur above the extension, mediums will offer enough clearance.
Tim